The invention relates to a method for recording contour data and/or optical properties of a three-dimensional semi-transparent object, especially a semi-transparent object in the dental area, such as a tooth or tooth restoration, on the basis of an interference and/or autocorrelation measurement, whereby                a bundle of rays from at least one light source of short coherence length is generated,        the bundle of rays is passed through a beam splitter and is preferably guided to the object through a focusing optical system,        a reference beam is split off in the beam splitter from the bundle of rays and is reflected by a reference mirror movable along the reference beam, whereby by moving the reference mirror, a position relative to a signal gaining surface is fixed relative to the object, and        the beam reflected from the object and from the reference mirror are brought together in the beam splitter and transferred into an image sensor having pixels, whereby temporally and/or spatially altered signal patterns can be recorded upon passing through the signal recovering surface.        
Furthermore, the invention makes reference to a device for recording contour data and/or optical properties of a three-dimensional semi-transparent object, especially a semi-transparent object in the dental area such as a tooth or tooth restoration, including at least one light source of short coherence length for generating a bundle of rays, a radiation component guiding the bundle of rays to the object through a focusing optical system on the one hand, and on the other into a beam splitter splitting up into a beam component leading to an adjustable reference mirror as well as an image sensor having pixels, which can be acted upon by the object and radiation reflected from the reference mirror and the beam splitter.
A method of the aforementioned type is described in German Patent DE-A-43 09 056, for example. With the known process, it is a matter of an interferometric method for ascertaining the distance and the scattering intensity of scattering points. These are illuminated by a broad band, spatially partially coherent light source and are located in one arm of an interferometer. An incandescent lamp or a super luminescence diode are indicated as light source. The light is separated into a spectrum and the output of the interferometer and information on the distance and the scattering intensity is ascertained on the basis of the brightness distribution in the spectrum. The disadvantage with the described method is that the resolution in the z direction, that is, into the depth of the object, is restricted.
In the article by Prof. G. Häsler: ““COHERENCE RADAR”—an Optical 3D Sensor with an Exactitude of 1 μm,” LASER INFO EXCHANGE, No. 36/April 1999, Association of German Engineers Technology Center, a method and a device for measuring a surface are described. The measuring principle rests upon white light interferometry, whereby local speckles are generated by a particular illumination selectively so that even the most distinct optically raw objects, such as milled surfaces or rubber, can be measured interferometrically. According to the method, one basically compares the length of the path of light for each object point with the length of the corresponding reference path of the interferometer. Only when the path lengths are approximately equal does an information contrast arise in the corresponding image point. While the sensor is moving toward the object, the point in time of the maximal interference contrast is determined individually for each image point and the respective sensor position is stored in memory.
A method and a device are known from German Patent DE-A-40 34 007, whereby the coating of the object is provided for obtaining three-dimensional data to avoid disturbing scattered radiation from the depth of a semi-transparent object such as, for example, a tooth or a dental filling which prevents this scattered radiation. This layer must nonetheless be applied by the dentist. This is thus an additional operation, which moreover can lead to irritations of the patient's respiratory passages due to the aspiration of dust articles in the event large areas of the dental corona are powdered.
In U.S. Pat. No. 6,697,164, a method and device are described, whereby the influence of a scatter beam is reduced through a confocal optical system. With this method, an array of incident light rays is guided into an optical beam path which is guided though a focusing optical system to a test surface. The focusing optical system defines one or more focal planes in front of the test surface in a position which can be changed by the optical system, whereby each light ray has its focus in reference to one or more focal planes. The rays generate a manifold of light spots on the contour. The intensity of each of these light spots is recorded. The steps mentioned above are repeated several times, whereby each time the position of the focal plane is altered relative to the contour. A light-point specific position is determined for each of the light spots which corresponds to a position of the respective focal plane which leads to a maximal measured intensity of a respective reflected light ray. Data are generated on the basis of the light spot-specific positions which represent the topology of the contour.
The described device for recording a surface topology of a region of a three-dimensional structure includes a probe with a contour to be scanned. Furthermore, a light source for generating an array of incident light rays which is transferred to the structure along an optical pathway is provided in order to generate light spots on the region. A light-focusing optical system defines one or more focal planes before the sample structure in a position which can be altered by the optical system. Each light ray has its focus on one or more focal planes. Furthermore, a displacement mechanism is linked with the focusing optical system in order to move this relative to the structure along the axis which is defined by the incident light rays. Moreover, a detector is provided with an array of sensor elements for measurement of the intensity of each of a large number of light rays which are reflected from the light spots opposite to the incident light. A processor is linked with the detector in order to ascertain a light spot-specific position for each light ray. Since a reflected light ray reaches the maximal intensity when the reflection position is situated in the focal plane, its specific position can be ascertained therewith. Data on the topology of the region are generated on the basis of the ascertained light spot-specific positions.
The influence of scattered radiation can be significantly reduced by using a confocal optical system from the aforementioned U.S. Pat. No. 6,697,194 B1.
A process and a device for measuring the contour data of an object can be derived from WO-A-95/33971. Here the interferometer principle is used, whereby a light source of coherence length is used. In order to subject the object to the action of light in sufficient spatial extension, there exists the possibility of expanding the light originating from a light source. The light rays running in the bundle of rays are nonetheless not separated from one another, but in part overlap one another.
A method for measuring dimensionings or optical properties of biological samples is known from U.S. Pat. No. 5,321,501, whereby the interferometer principle is likewise used. According to one embodiment, rapidly changing biological samples can be acted upon with radiation from different optical sources at the same time. Each ray source is allocated a detector. Several regions of the sample can be scanned parallel and simultaneously.